"Clean room" test for a "copy on write" problem leading to bugs #113

and #928. Under certain conditions a fork()ed child process can
write to the parent process' memory.
A fix follows...


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@20401 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/tests/system/kernel/Jamfile

@@ -3,10 +3,17 @@ SubDir HAIKU_TOP src tests system kernel ;
 UsePrivateHeaders kernel ;
 UseHeaders $(TARGET_PRIVATE_KERNEL_HEADERS) : true ;
 
+SimpleTest cow_bug113_test : cow_bug113_test.cpp ;
+
 SimpleTest fibo_load_image : fibo_load_image.cpp ;
 SimpleTest fibo_fork : fibo_fork.cpp ;
 SimpleTest fibo_exec : fibo_exec.cpp ;
 
+SimpleTest lock_node_test :
+	lock_node_test.cpp
+	: be
+;
+
 SimpleTest port_close_test_1 : port_close_test_1.cpp ;
 SimpleTest port_close_test_2 : port_close_test_2.cpp ;
 
@@ -22,16 +29,11 @@ SimpleTest port_wakeup_test_7 : port_wakeup_test_7.cpp ;
 SimpleTest port_wakeup_test_8 : port_wakeup_test_8.cpp ;
 SimpleTest port_wakeup_test_9 : port_wakeup_test_9.cpp ;
 
-SimpleTest transfer_area_test : transfer_area_test.cpp ;
-
 SimpleTest syscall_time : syscall_time.cpp ;
 
-SimpleTest yield_test : yield_test.cpp ;
+SimpleTest transfer_area_test : transfer_area_test.cpp ;
 
-SimpleTest lock_node_test :
+SimpleTest yield_test : yield_test.cpp ;
-	lock_node_test.cpp
-	: be
-	;
 
 SimpleTest wait_test_1 : wait_test_1.c ;
 SimpleTest wait_test_2 : wait_test_2.cpp ;

src/tests/system/kernel/cow_bug113_test.cpp

@@ -0,0 +1,64 @@
+#include <stdio.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#include <OS.h>
+
+const char* kInitialValue = "/dev/null";
+const char* kChangedValue = "Argh!";
+
+int
+main(int argc, const char* const* argv)
+{
+	thread_id parent = find_thread(NULL);
+
+	char* globalVar = NULL;
+	area_id area = create_area("cow test", (void**)&globalVar,
+		B_ANY_ADDRESS, B_PAGE_SIZE, B_NO_LOCK, B_READ_AREA | B_WRITE_AREA);
+	if (area < 0) {
+		printf("failed to create area\n");
+		return 1;
+	}
+
+	strcpy(globalVar, kInitialValue);
+
+	printf("[%ld] parent: before fork(): globalVar(%p): \"%s\"\n", parent,
+		globalVar, globalVar);
+
+	pid_t child = fork();
+	if (child == 0) {
+		// child
+		child = find_thread(NULL);
+
+		// let the kernel read access the page
+		struct stat st;
+		stat(globalVar, &st);
+
+		printf("[%ld] child: after kernel read: globalVar: \"%s\"\n",
+			child, globalVar);
+
+		// write access the page from userland
+		strcpy(globalVar, kChangedValue);
+
+		printf("[%ld] child: after change: globalVar: \"%s\"\n", child,
+			globalVar);
+
+	} else {
+		// parent
+
+		// wait for the child
+		status_t exitVal;
+		while (wait_for_thread(child, &exitVal) == B_INTERRUPTED);
+
+		// check the value
+		printf("[%ld] parent: after exit child: globalVar: \"%s\"\n",
+			parent, globalVar);
+
+		if (strcmp(globalVar, kInitialValue) == 0)
+			printf("test OK\n");
+		else
+			printf("test FAILED: child process changed parent's memory!\n");
+	}
+
+	return 0;
+}